This document is the TN 5.01_C Recommended Use For Trench Boxes. Introduction, considerations and installation provided with a figure and descriptors.

Trench boxes provide a safer work area to install pipe in deep trenches, restricted right-of-ways, or in soils that have insufficient stability. This technical bulletin provides guidelines on how to maximize the structural stability and alignment of the ADS pipe system while using a trench box. While these guidelines will work for most cohesive and noncohesive native soils, highly unusual soil conditions may require further investigation or different techniques.

OSHA regulations should be carefully followed for all aspects of pipe installation, including those that involve trench boxes. Some installations may not require trench boxes if the trench sidewall can be sloped adequately. The design engineer should provide specific guidance on acceptable slopes, but in no case should the trench wall slope be greater than the angle of repose of the native soil. The length of the trench box should be suitable for the pipe length. Standard length for ADS N-12® IB is 6m.

The most effective way to maintain a sound system is to provide a ‘subtrench’ within which to place the pipe and backfill. The bottom of the trench box should be placed no more than 600 mm (24”) from the bottom of the work surface, in accordance with OSHA regulation 1926.652(g)(2). This may require the trench box be raised during pipe installation to conform with both OSHA requirements and to properly backfill and compact the soil around the pipe. Backfill and compact according to the design specifications within the subtrench. When possible, without disturbing the pipe or backfill, the trench box can be pulled along the top edge of the subtrench. In some cases, it may be necessary to move the trench box multiple times to obtain the required compaction of the material in the soil envelope. In either case, it is paramount to achieve the necessary backfill placement and compaction for a quality installation. Figure for a typical sub trench installation provided.